<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        let i = prompt("请输入")
        if(i >= 90){
            alert("A")
        }else if(i<90&&i>=80){ 
            alert("B")
        }else if(i<80&&i>=70){
            alert("C")
        }else if(i<70&&i>=60){
            alert("D")
        }else if(i<60){
            alert("E")
        }
    </script>
</body>
</html>